Mechanical pitch control

ABSTRACT

A concrete finishing machine having a rotatable trowel blade assembly and a mechanism for controllably adjusting the pitch of the trowel blades relative to a wet concrete surface on which the blades rest. The machine&#39;s engine&#39;s drive shaft rotation itself is utilized to create changes in pitch.

[0001] This application claims priority from U.S. Application No.60/349,480, filed Dec. 31, 2002, having the same inventors, thedisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to concrete finishing machines,and, more particularly, to apparatus for controllably adjusting thepitch of the trowel blades of such machines.

[0004] 2. Background Information

[0005] Concrete finishing machines have been used for many years tolevel and finish large concrete pads. Such machines typically include arotatable trowel blade assembly having a plurality (e.g., three or four)of generally planar trowel blades mounted on trowel arms projectingradially outwardly from a common hub, all of which are rotated by agasoline-powered engine. The trowel blades rest directly on the concretesurface to be finished and support the machine's entire weight.

[0006] Concrete finishing machines typically further include means forcontrollably pivoting the trowel blades about their respective radialaxes, to change their pitch relative to the concrete surface to befinished. Changing the blades' pitch correspondingly changes theproportion of blade surface contacting the concrete surface, such thatthe machine's weight is supported by a larger or smaller area of thesurface.

[0007] In use, the machine makes several passes over the concretesurface as the concrete hardens, with the blade pitch being speciallyselected for each pass. In the initial pass, when the concrete is stillvery wet and plastic, the blade pitch is usually adjusted to besubstantially parallel with the concrete surface, thereby lying flatupon it and spreading the machine's weight over a maximum surface area.In subsequent passes, as the concrete hardens and becomes less plastic,the blade pitch is progressively increased, with the pitch used in thefinal pass sometimes being as much as about 30 degrees.

[0008] Improvements in recent concrete formulations have made someconcrete slabs include pockets or areas of varying plasticity. In suchsituations, it is necessary to rapidly adjust the trowel blade pitch inorder to produce the desired finish. It is also necessary to adjust thetrowel blade pitch when the machine is being moved to an adjacent areawhere the concrete is at a different stage of hardness. In thissituation, which frequently occurs when very large concrete pads arebeing formed, the blade pitch must be adjusted very rapidly.

[0009] In the past, the pitch of the trowel blades was typicallyadjusted using a thrust collar that pushed downwardly on fingersprojecting upwardly from the rear sides of the respective trowel arms.Typically, such a downward force on the thrust collar is provided by ayoke or fork that is pivotally secured to the machine's frame andconnected to an actuator means adjacent the device's handlebars. Byoperating the actuator means, the pitch yoke is manipulated therebyapplying (or removing) a force on the thrust collar. Examples of such ayoke and thrust collar pitch control can be seen in U.S. Pat. Nos.3,412,657 (Colizza et al.), 3,791,754 (Zochil), 4,232,980 (Tertinek etal.), 4,577,993 (Allen et al.), 4,673,311 (Whiteman, Jr.), and 5,405,216(Allen et al.).

[0010] A disadvantage to this use of yoke (or fork) is the fact that thethrust collar is depressed (or lifted) at two points, namely by itscontact with the ends of the two arms of the yoke. Having pressureapplied at two points can lead to slight tilting of the thrust collarand thereby resulting in wear between the thrust collar and the driveshaft and/or the thrust collar wear bushing inserted between the driveshaft and the thrust collar. What is needed is a method of moving athrust collar that eliminates this wear caused be the application ofpressure by a yoke.

[0011] A second disadvantage with a yoke and thrust collar system is thenecessity to use cables, chains and other means of moving the yoke. Inorder to conceal and protect these means, they typically extend from thehandlebars to pitch controller via the inside of the handle. Because ofthis, such a handle is limited in minimum diameter and is unable to befoldable. What is needed is the ability to fold the handle.

[0012] A third disadvantage to the prior art yoke and thrust collarsystem is the fact that the user must physically supply the forcenecessary to move the thrust collar into engagement with the fingers ofthe arms of the blades. Various mechanical means are shown in the priorart which help reduce the amount of force required, but the fact remainsthat the user is still required to physically depress or lift the thrustcollar. What is needed is a pitch controller that does not require theuser to physically manipulate the thrust collar.

[0013] A fourth disadvantage to many renditions of the old yoke systemis the convenience of the user. The trailing edge of each trowel blade,which contacts the concrete surface on which the machine rests, isspaced from the blade's pivot axis. Any change in blade pitch thereforetransfers the machine's weight by raising or lowering the machine on thesurface. Since the machine is generally quite heavy, usually weighingseveral hundred pounds, the screw handle used for blade pitch adjustmentmust have threads with a very small pitch to permit the operator torotate it conveniently. Consequently, the blade pitch adjustment can bemade only very slowly. This has been proven to be unsatisfactory in manysituations. Some concrete finishing machines have overcome the slowpitch adjustment afforded by the screw handle described above byreplacing the screw handle with a long lever attached to the machine'sframework. Although this configuration permits a rapid adjustment of theblade pitch, it is not generally convenient to use. This is because thelever requires large movements for lever advantage and because the leveris not conveniently located on the machine handle itself and thusrequires the operator to control the machine using merely one hand andunsteady footing. What is needed is a means of changing pitch whichrequires less digital manipulation than the prior art methods.

[0014] It should be appreciated from the foregoing that there is asignificant need for a concrete finishing machine having a trowel bladeadjustment apparatus that can be used by the operator to mechanicallyadjust the trowel blade pitch, yet is simple in construction andconvenient to use. The present invention fulfills this need.

[0015] Additional objects, advantages and novel features of theinvention will be set forth in part in the description which follows andin part will become apparent to those skilled in the art uponexamination of the following or may be learned by practice of theinvention. The objects and advantages of the invention may be realizedand attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

SUMMARY OF THE INVENTION

[0016] The present invention is an improved pitch controller. Such apitch controller particularly configured for use with a concretefinishing trowel. The preferred embodiment utilizes the existingmechanical rotation of the drive shaft and/or attached rotors to serveas the source of the force required to raise and lower the weight of thetrowel while the pitch of the blades is adjusted. Thus, the presentinvention includes any means of using the rotation of the drive shaftand/or attached rotors to adjust the pitch of the blades. For instance,using the drive shaft's rotation to maneuver a thrust collar away fromthe trowel transmission and into engagement with the blade pitchmechanism of the trowel, thereby increasing or decreasing the pitch ofthe attached blades.

[0017] In one embodiment, the present invention comprises an improvedconcrete finishing trowel or machine. This trowel having a drive means(i.e., engine, motor, turbine, etc.) having extending therefrom a driveshaft. This drive shaft connecting with and configured to rotate arotatable blade assembly. This rotatable blade assembly adapted tofinish a concrete surface. This rotatable blade assembly having agenerally vertical axis of rotation and a plurality of radially spacedapart concrete finishing blades extending outwardly from said verticalaxis for frictionally contacting the concrete surface. These blades eachdefining a longitudinal axis generally perpendicular to the verticalaxis.

[0018] The trowel further having a pitch controller for varying thepitch of the blades by rotating them about their longitudinal axis. Thispitch controller utilizing the rotation of the drive shaft to rotate theblades. This pitch controller comprising a thrust collar, a nut, and abearing. The thrust collar comprising a plate configured to beardownwardly on the rotatable blade assembly thereby varying the pitch ofthe blades by rotating them about their longitudinal axis. The saidthrust collar further comprising a hollow shaft able to receive thedrive shaft therethrough, this hollow shaft having an exterior surfacewhich is threaded.

[0019] The pitch controller's nut being configured for threading ontothe exterior surface of the thrust collar. This nut having an uppersurface for supporting a bearing. This bearing configured to support thelower surface of the drive means or other component of the body of thetrowel.

[0020] Finally, the pitch controller comprises a clutch for selectivelyengaging and disengaging the pitch controller. In use, the nut can bethreaded in a first direction on the thrust collar and towards thethrust collar plate. Likewise, the nut can be threaded in an opposite,second direction on the thrust collar and away from the thrust collarplate. Travel in the first direction resulting in a reduction in thedegree of downward bearing upon the rotatable blade assembly by thethrust collar plate thereby resulting in a decrease in pitch. Travel inthe second direction resulting in an increase in the degree of downwardbearing upon the rotatable blade assembly by the thrust collar platethereby resulting in an increase in pitch.

[0021] In this preferred embodiment, the drive means drives the driveshaft thereby rotationally driving the thrust collar and the rotatableblade assembly. The clutch is configured to stop the nut while the drivemeans is driving, thereby resulting in travel in the second directionand moving the thrust collar away from the nut. Likewise, the clutch isconfigured to transmit the rotation of the thrust collar to achievetravel in the second direction thereby drawing the thrust collar nearerthe nut. This is particularly seen where the diameter of the thrustcollar is greater than the nut, whereby rotation of the thrust collarresults in expedited rotation of the nut.

[0022] Still other objects and advantages of the present invention willbecome readily apparent to those skilled in this art from the followingdetailed description wherein I have shown and described only thepreferred embodiment of the invention, simply by way of illustration ofthe best mode contemplated by carrying out my invention. As will berealized, the invention is capable of modification in various obviousrespects all without departing from the invention. Accordingly, thedrawings and description of the preferred embodiment are to be regardedas illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a perspective view of one embodiment of a power trowelutilizing the present invention.

[0024]FIG. 2 is an exploded, side view of a first embodiment of thepresent invention.

[0025]FIG. 3 is a side view of a second embodiment of the presentinvention shown with no pitch applied to the blades.

[0026]FIG. 4 is a side view of the embodiment of FIG. 3, showing pitchapplied to the blades

[0027]FIG. 5 is a cross-sectional view of one embodiment of a nut of thepresent invention.

[0028]FIG. 6 is a cross-sectional view of one embodiment of a thrustcollar of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] While the invention is susceptible of various modifications andalternative constructions, certain illustrated embodiments thereof havebeen shown in the drawings and will be described below in detail. Itshould be understood, however, that there is no intention to limit theinvention to the specific form disclosed, but, on the contrary, theinvention is to cover all modifications, alternative constructions, andequivalents falling within the spirit and scope of the invention asdefined in the claims.

[0030] Referring initially to FIGS. 1 and 2, for purposes ofillustration, the present invention is embodied in a concrete finishingmachine 80 of the kind that includes a rotatable trowel blade assemblyor spider 86 rotatably driven by a suitable drive means or engine 82.This drive means having a drive shaft 84 which is typically keyed orlocked into the hub 95 of the trowel blade assembly 86. The trowel bladeassembly 86 includes a plurality (e.g., three or four) ofuniformly-spaced trowel blade arms 90 projecting radially outwardly froma common hub 94, each arm 90 carrying a separate substantially planarconcrete finishing or trowel blade 88.

[0031] The blades 88 are configured to rest directly on a wet,semi-plastic concrete surface 19 to be finished and these blades 88support the machine's 80 entire weight. The blades 88 are all pivotableabout their respective radial axes to typically change their pitchrelative to the concrete surface 19 over a range typically extendingfrom substantially 0 degrees to about 30 degrees. This pivoting changesthe area of the blade surface contacting the concrete and thus changesthe pressure applied to the concrete. The pivoting also correspondinglyraises or lowers the machine on the surface.

[0032] Referring now to FIGS. 2-4, this rotatable trowel blade assemblyor spider 86 has a central blade hub 94 to which said pivotable blades88 attach. This hub 94 having a shaft connection 95 extendingtherethrough allowing the hub 94 to be fixed upon the drive shaft 84descending from the drive means of the concrete finishing machine ortrowel, the drive shaft 84 able to be inserted into the shaft connection95, with a pin, screw, key or other connection connecting the driveshaft to the hub at said drive shaft connection 95.

[0033] The thrust collar 22, preferably lined with an oil-impregnatedthrust collar bushing 97 (shown in FIG. 6), is fitted over the hub(before the shaft is connected to the hub). This thrust collar 22 ableto be moved upwards or downwards upon said hub. The replaceablility ofsaid bushing 97 allowing for easy reconditioning of the trowel. In sucha manner, the bushing engages the hub in a manner that allows the thrustcollar to more efficiently slide up and down upon the hub. Of course,the utilization of such a bushing is optional.

[0034] Referring now to FIGS. 2-4, and 6, the thrust collar 22 of thepresent invention 10 has a geared rim 23 and an elongated, threaded neck25. This neck 25 defining a hollow shaft 26 therethrough (FIG. 6) forreceiving the bushing 97 and/or the upper portion of the hub 94. Thistreaded neck 25 for receiving thereon a nut 30 having a portioncontaining interior threads 36. The thrust collar 22 defining a thrustcollar body or plate 24 for cooperating with the fingers 92 and/or arms90 of the spider (blade assembly) 86 to increase or decrease the pitchof the attached concrete finishing blades 88.

[0035] Optionally, as shown in FIGS. 2-4, the thrust collar 22 mayadditionally comprise a pin 40 extending from said plate 24 generallyperpendicular to said plate. This pin 40 for contacting said bladeassembly (spider) 86, thereby keeping the thrust collar 22 from rotatingseparately from the blade assembly 86, thereby reducing wear and tearupon the thrust collar and fingers/arms of the blade assembly. Thus, oneembodiment of the present invention may comprise a standard thrust plateutilized with the prior art yoke style of engagement which includes apin 40 extending from said plate, generally perpendicular to said plate.

[0036] The nut 30 is provided having a geared rim 34 and a threadedinner surface 36 able to receive therein the threading of the thrustcollar's threaded neck 28. This nut 30 is able to travel along thethreaded neck 28 of the thrust collar 22. The upper surface 32 of thenut 30 is configured to support a bearing 48 which in turn supports thebottom 98 of the transmission case 96, the drive means lower surface oranother portion of the concrete finishing trowel.

[0037] In use, the drive shaft 84 turns the spider 86 and the thrustcollar 22. The nut 30, being threaded onto the thrust collar 22, rotateswith the thrust collar 22 by default. As shown in FIG. 4, to increasethe pitch of the blades 88, a user would manipulate the control handleto engage the clutch 50 into a first position via the interconnector 72to stop the nut 30. In the preferred embodiment, a pawl 52 is utilizedto stop the rotation of the nut 30. Stopping the rotation of the nut 30causes the nut 30 to unscrew (screw up on the thrust collar neck 25).Because the nut 30 is already topped out against the bearing 48 whichsupports the transmission case bottom 98 or other portion of the trowel,the thrust collar 22 actually unscrews out of the nut 30 downwardscarrying the rotation of drive shaft 84. The preferred clutch 50 isshown in the figures, however other clutches and manners of engagingand/or disengaging the invented pitch controller are also envisioned.The preferred clutch is a manner of stopping the rotation of the nutwhile allowing the thrust collar to continue to rotate.

[0038] As the thrust collar 22 unscrews downwards from the nut, theunderside 24 of the thrust collar plate bears downwardly on the bladepitch mechanism 89 of the trowel blades, namely upon the fingers 92.This downward force upon the fingers 92 causes the arms 90 to rotateabout their respective radial axes and thus increases the pitch of theblades 88. When the desired degree of pitch is obtained, the user wouldmanipulate the control handle to cause the gear 54 to release the nut30, thereby moving the clutch 50 into its neutral position.

[0039] As shown in FIG. 3, to reverse this process and decrease thepitch, the clutch 50 would be moved by the user via the control handleand attached interconnector 72 to the clutch's second position. In thissecond position, a gear 54 (or connected pair of gears) having a coupleof different diameters would be engaged against the geared rims 23, 34of the thrust collar 22 and the nut 30. This gear 54 used to make thenut 30 rotate at a speed greater than the rotation of the thrust collar22, thereby resulting in the thrust collar 22 screwing back into the nut30.

[0040] At any desired point, the user could disengage this gear 54 bymoving the clutch 50 into “neutral” thereby stopping the screwing backin. This process allowing for an infinite adjustment in the reduction ofthe pitch. Allowing for the total screwing back in of the thrust collarwould preferably result in generally zero degree of pitch.

[0041] Referring back to FIG. 1, for safety, a guard ring 21 encirclesthe peripheral tips of the trowel blades. An operator (not shown) canguide and control the machine using a machine handle 68, preferablyhaving one or more handlebars 69. In the preferred embodiment, the pitchof the trowel blades 88 relative to the concrete surface 19 on whichthey rest can be manually adjusted using a control lever 70 pivotallysecured to the machine handle 68. This pitch adjustment is madeaccording to the concrete's hardness or plasticity, beginning with theblades lying substantially flat on the surface when the concrete is verywet or plastic and ending with the blades at a substantial angle (e.g.,30 degrees) when the concrete has substantially hardened. The controllever 70 is connected to the rotatable trowel blade assembly 86 throughuse of a interconnector 72. However, any and all other manners ofengaging and disengaging the clutch is also envisioned.

[0042] Referring now to FIG. 4, to transform movement of theinterconnector 72 into pivoting of the individual trowel blades 88, thetrowel blade assembly 86 includes an improved pitch controller 10 havinga thrust collar 22 overlaying the blade hub 94. In addition, each trowelblade includes an outwardly and upwardly projecting arm 90, this armconfigured to act as a crank for pivoting the blade about its radialaxis. The head of an adjustment screw or “finger” 92 projects upwardlyfrom the end of the arm for engagement with the underside of the thrustcollar.

[0043] In the embodiment shown, the interconnector 72 is connected to aclutch 50 for selectively engaging and disengaging the pitch controller10. In the preferred embodiment, the clutch 50 has three modes, namely“increase pitch,” “maintain pitch” and “decrease pitch.”

[0044] When the clutch 50 is, via said control handle 70 and saidinterconnected interconnector 72, in the “increase pitch” mode, thepitch controller is engaged to increase pitch. In the preferredembodiment, when in this mode, the clutch 50 engages a pawl 52 whichstops the rotation of the nut 30. Stopping the rotation of the nut, asdiscussed above, causes the thrust collar 22 to unscrew out of the nut30 thereby resulting in the thrust collar 22 depression of the fingers92 of the blade pitch mechanism 89 resulting in the rotation of thetrowel blades about their radial axis, increasing pitch. This action isparticularly shown in FIG. 4.

[0045] When the clutch is, via said control handle 70 and saidinterconnected interconnector 72, in the neutral (“maintain pitch”)mode, the pitch controller is left in its current degree of pitch. Inthe preferred embodiment, in such a mode, the nut 30 remains in a fixedlocation upon the treads of the thrust collar, rotating at the exactsame rate as the thrust collar, maintaining the position of the trustcollar and thus the current degree of pitch.

[0046] When the clutch 50 is, via said control handle 70 and saidinterconnected interconnector 72, in the “decrease pitch” mode, thepitch controller 10 is engaged to decrease pitch. In the preferredembodiment, when in this mode, the clutch 50 engages a gear 54 whichengages both the geared rim 23 of the thrust collar and the geared rim34 of the nut. This dual gear 54 geared to cause the nut 30 to rotate ata rate greater than the rotation of the thrust collar 22, therebyscrewing the thrust collar 22 back into the nut 30. This results in thethrust collar 22 exerting less pressure downwards on the fingers 92 ofthe blade pitch mechanism 89, thereby resulting in a reduction in therotation of the trowel blades about their radial axis, decreasing pitch.

[0047] In another embodiment, the present invention could utilize rubberrollers and coated surfaces to achieve the same effect as theutilization of clutch gear or cog and the geared edge of the nut and thegeared edge of the thrust collar.

[0048] Another embodiment of the present invention comprises a thrustcollar having a neck having a threaded outer surface.

[0049] Another embodiment of the present invention comprises a thrustcollar having a generally perpendicular pin extending therefrom forcontacting the spider (rotatable blade assembly).

[0050] Because the prior art devices required engagement anddisengagement mechanisms which at least partially transit through ahollow handle, the present invention comprises, in another embodiment, apower trowel having a folding handle, with or without the invented pitchcontroller.

[0051] While there is shown and described the present preferredembodiment of the invention, it is to be distinctly understood that thisinvention is not limited thereto but may be variously embodied topractice within the scope of the following claims. From the foregoingdescription, it will be apparent that various changes may be madewithout departing from the spirit and scope of the invention as definedby the following claims.

We claim:
 1. A concrete finishing trowel comprising: a drive meanshaving extending therefrom a drive shaft, said drive shaft connectingwith and configured to rotate a rotatable blade assembly; a rotatableblade assembly adapted to finish a concrete surface, said rotatableblade assembly having a generally vertical axis of rotation and aplurality of radially spaced apart concrete finishing blades extendingoutwardly from said vertical axis for frictionally contacting saidconcrete surface, said blades each defining a longitudinal axisgenerally perpendicular to said vertical axis; a pitch controller forvarying the pitch of said blades by rotating them about theirlongitudinal axis, said pitch controller utilizing the rotation of saiddrive shaft to rotate said blades about their longitudinal axis; and, aclutch for selectively engaging and disengaging said pitch controller.2. The trowel of claim 1, wherein said pitch controller comprises athrust collar, said thrust collar having a plate configured to beardownwardly on said rotatable blade assembly thereby varying the pitch ofsaid blades by rotating them about their longitudinal axis.
 3. Thetrowel of claim 2, wherein said thrust collar further comprises a hollowshaft able to receive said drive shaft therethrough, said hollow shafthaving an exterior surface, said exterior surface threaded.
 4. Thetrowel of claim 3, wherein said pitch controller further comprises anut, said nut configured for threading onto said thrust collar exteriorsurface, said nut having an upper surface.
 5. The trowel of claim 4,wherein said pitch controller further comprises a bearing configured tosupport a drive means lower surface on said nut upper surface.
 6. Thetrowel of claim 5, wherein said nut can be threaded in a first directionon said thrust collar and towards said thrust collar plate, and whereinsaid nut can be threaded in an opposite, second direction on said thrustcollar and away from said thrust collar plate.
 7. The trowel of claim 6,wherein travel in said first direction results in a reduction in thedegree of downward bearing upon said rotatable blade assembly by saidthrust collar plate thereby resulting in a decrease in pitch.
 8. Thetrowel of claim 7, wherein travel in said second direction results in anincrease in the degree of downward bearing upon said rotatable bladeassembly by said thrust collar plate thereby resulting in an increase inpitch.
 9. The trowel of claim 8, wherein said drive means drives saiddrive shaft thereby rotationally driving said thrust collar and saidrotatable blade assembly.
 10. The trowel of claim 9, wherein said clutchis configured to stop said nut while said drive means is driving therebyresulting in travel in said second direction and moving said thrustcollar away from said nut.
 11. The trowel of claim 10, wherein saidclutch is configured to transmit the rotation of said thrust collar toachieve travel in said second direction thereby drawing the thrustcollar nearer said nut.
 12. A concrete finishing trowel comprising: adrive means having extending therefrom a drive shaft, said drive shaftconnecting with and configured to rotate a rotatable blade assembly; arotatable blade assembly adapted to finish a concrete surface, saidrotatable blade assembly having a generally vertical axis of rotationand a plurality of radially spaced apart concrete finishing bladesextending outwardly from said vertical axis for frictionally contactingsaid concrete surface, said blades each defining a longitudinal axisgenerally perpendicular to said vertical axis; a pitch controller forvarying the pitch of said blades by rotating them about theirlongitudinal axis, said pitch controller utilizing the rotation of saiddrive shaft to rotate said blades about their longitudinal axis, saidpitch controller comprising a thrust collar, a nut, and a bearing; saidthrust collar comprising a plate configured to bear downwardly on saidrotatable blade assembly thereby varying the pitch of said blades byrotating them about their longitudinal axis, said thrust collar furthercomprising a hollow shaft able to receive said drive shaft therethrough,said hollow shaft having an exterior surface, said exterior surfacethreaded; said nut configured for threading onto said thrust collarexterior surface, said nut having an upper surface; and said bearingconfigured to support a drive means lower surface on said nut uppersurface; and a clutch for selectively engaging and disengaging saidpitch controller.
 13. The trowel of claim 12, wherein said nut can bethreaded in a first direction on said thrust collar and towards saidthrust collar plate, and wherein said nut can be threaded in anopposite, second direction on said thrust collar and away from saidthrust collar plate.
 14. The trowel of claim 13, wherein travel in saidfirst direction results in a reduction in the degree of downward bearingupon said rotatable blade assembly by said thrust collar plate therebyresulting in a decrease in pitch.
 15. The trowel of claim 14, whereintravel in said second direction results in an increase in the degree ofdownward bearing upon said rotatable blade assembly by said thrustcollar plate thereby resulting in an increase in pitch.
 16. The trowelof claim 15, wherein said drive means drives said drive shaft therebyrotationally driving said thrust collar and said rotatable bladeassembly.
 17. The trowel of claim 16, wherein said clutch is configuredto stop said nut while said drive means is driving thereby resulting intravel in said second direction and moving said thrust collar away fromsaid nut.
 18. The trowel of claim 17, wherein said clutch is configuredto transmit the rotation of said thrust collar to achieve travel in saidsecond direction thereby drawing the thrust collar nearer said nut. 19.A concrete finishing trowel comprising: a drive means having extendingtherefrom a drive shaft, said drive shaft connecting with and configuredto rotate a rotatable blade assembly; a rotatable blade assembly adaptedto finish a concrete surface, said rotatable blade assembly having agenerally vertical axis of rotation and a plurality of radially spacedapart concrete finishing blades extending outwardly from said verticalaxis for frictionally contacting said concrete surface, said blades eachdefining a longitudinal axis generally perpendicular to said verticalaxis; a pitch controller for varying the pitch of said blades byrotating them about their longitudinal axis, said pitch controllerutilizing the rotation of said drive shaft to rotate said blades abouttheir longitudinal axis, said pitch controller comprising a thrustcollar, a nut, and a bearing; said thrust collar comprising a plateconfigured to bear downwardly on said rotatable blade assembly therebyvarying the pitch of said blades by rotating them about theirlongitudinal axis, said thrust collar further comprising a hollow shaftable to receive said drive shaft therethrough, said hollow shaft havingan exterior surface, said exterior surface threaded; said nut configuredfor threading onto said thrust collar exterior surface, said nut havingan upper surface; said bearing configured to support a drive means lowersurface on said nut upper surface; and a clutch for selectively engagingand disengaging said pitch controller; wherein said nut can be threadedin a first direction on said thrust collar and towards said thrustcollar plate, and wherein said nut can be threaded in an opposite,second direction on said thrust collar and away from said thrust collarplate; wherein travel in said first direction results in a reduction inthe degree of downward bearing upon said rotatable blade assembly bysaid thrust collar plate thereby resulting in a decrease in pitch;wherein travel in said second direction results in an increase in thedegree of downward bearing upon said rotatable blade assembly by saidthrust collar plate thereby resulting in an increase in pitch; whereinsaid drive means drives said drive shaft thereby rotationally drivingsaid thrust collar and said rotatable blade assembly; wherein saidclutch is configured to stop said nut while said drive means is drivingthereby resulting in travel in said second direction and moving saidthrust collar away from said nut; and wherein said clutch is configuredto transmit the rotation of said thrust collar to achieve travel in saidsecond direction thereby drawing the thrust collar nearer said nut.